peer-reviewed article bioresources · peer-reviewed article bioresources.com xia et al. (2014)....

PEER-REVIEWED ARTICLE bioresources.com

Xia et al. (2014). “Modeling straw ring-die briquetting,” BioResources 9(4), 6316-6328. 6316

Modeling of a Straw Ring-die Briquetting Process

Xianfei Xia, Yu Sun,* Kai Wu, and Qinghai Jiang

Efficient utilization of biomass resources is crucial for providing renewable energy and mitigating the risk of environmental pollution caused by crop straw burning in China. Straw ring-die briquetting forming is a convenient densification technology to make the low density biomass into briquette fuel; however, the energy consumption of this process is still a challenge. Productivity and torque modeling were carried out in this study on the basis of theoretical derivation. Generally, the straw briquetting process is divided into a compression deformation stage and an extrusion forming stage with the die structure (ring die and roller radius ratio λ) and friction angle φ being the main factors that affect the productivity. Mechanical modeling based on material compaction and calculation modeling based on die-hole pressure were considered for the calculation of σαx in the torque model. A calculation case was then conducted according to the theoretical model, and actual productivity and torque testing were performed for validation purposes. Results show that this deduced productivity model is successful because the deviation is 4.61%. The torque model determined by the calculation model based on die-hole pressure had a better accuracy with a deviation of 6.76%.

Keywords: Briquetting; Straw; Productivity; Mechanical modeling; Torque

Contact information: School of Mechanical Engineering, Nanjing University of Science and Technology,

No. 200 Xiaolingwei, Nanjing 210094, China;

* Corresponding author: [email protected]

INTRODUCTION

With the growing energy crisis and environmental problems (Tuo 2013), utilization

of biomass has gained a lot of attention. Because straw contains a large amount of useful

lignin and cellulose, efficient utilization of this abundant resource is crucial for providing

bio-energy and mitigating the risk of environmental pollution. This research presents a

study on the analysis of machinery for handling biomass for energy generation, in particular

transforming straw materials to briquettes. The need for this transformation has been

widely justified, as shown by other works (Panwar et al. 2010). The transformation has two

processes: densifying the low density straw and rolling it to a form for easy transportation.

The device to make this transformation is called ring-die briquetting (R-D for short). The

R-D system has many advantages such as versatility and flexibility to different types of

low density straws compared with the system of screw bar pressing and piston pressing

(Stelte et al. 2012), but the shortcoming of high energy consumption during the briquetting

process still exists (Zhang et al. 2008).

For all the biomass briquetting systems, the average energy consumption is the most

important evaluation index; it is calculated by the ratio of power consumption and

productivity (Ståhl and Berghel 2011). Power consumption is the product of speed (ring

die rotational speed or roller rotational speed) and torque (Cong et al. 2013), while the

speed is generally determined in advance (Yao et al. 2013). When the raw material property



remains unchanged, the reasonable parameter design is the main way to reduce energy

consumption. So it is necessary to establish the productivity and torque model to describe

the energy consumption of the R-D system’s actual working process.

Some studies have focused on the forming mechanism (Adapa et al. 2013; Gillespie

et al. 2013), and others on fuel quality (Kaliyan and Morey 2010; Karunanithy et al. 2012).

Studies have reported on the energy consumption with this process in a laboratory setting

with a single pelleter unit (Ghadernejad and Kianmehr 2012; Hu et al. 2013; Song et al.

2014). It is well known that laboratory studies on such a process can hardly be extended to

the industrial setting. Hu (2013) and Holm et al. (2011) obtained the theoretical models to

describe the forming pressure by extrusion testing respectively; these models are the bases

of force analysis and torque calculation. Duan et al. (2013) made an optimization analysis

of energy consumption and productivity of the R-D briquetting machine by factory test,

but the corresponding theoretical calculation models were not established. Yao et al. (2013)

developed a new vertical R-D briquetting machine to increase productivity and reduce

energy consumption; however there was no theoretical calculation of its productivity; and

the forming pressure was considered to be constant in the power consumption analysis.

Although Ståhl and Berghel (2011) studied the energy consumption of a pilot-scale

production of wood fuel pellets, the testing object was a flat die machine.

Cong et al. (2013) and Wu et al. (2013) built up the productivity and torque models

of a biomass pellet mill; however the method to calculate the pressure in the forming zone

was not comprehensive enough. In addition, there are some obvious differences between a

biomass briquetting machine and a pellet mill: the ring die of pellet mill is the driving

component and it rotates under normal condition, while the ring die of a briquetting

machine is fixed on the frame, and the driving component is roller; the pellet mill ring die

is usually horizontal placement, whereas the briquetting machine ring die is vertical. The

motion state and force condition of the main working parts are various.

Therefore, the current models are not applicable. Modeling the R-D process to more

accurately predict its productivity and driving torque is very important in reasonably

designing or optimizing the R-D briquetting machine. The objective of this work was to

present a model to calculate the productivity and driving torque for the R-D process for

straw material. The paper is organized as follows: first, a brief introduction for the working

principle for the straw briquetting process is given. Then, the model for estimating

productivity rate and for computing the torque will be presented. Later, a case study with

the experiment on an industrial scale is presented to verify the model. Finally, some

conclusions are given.

EXPERIMENTAL

The Working Principle of the Straw R-D Process The working principle of the straw R-D process is shown in Fig. 1. The ring die is

fixed on the machine. When the straw material is fed into the cavity formed by the ring die

and press roller, the roller (driven by a spindle) starts to rotate and grab the material. The

material then is compressed and squeezed into the die holes gradually. Lignin and cellulose

contained in the raw material begins to soften and then bond together under the action of

frictional heat. After a specific holding time the straw is extruded out as a briquetting fuel

with a certain shape (diameter of 20 to 30 mm, length of 40 to 80 mm) and density (0.8 to

1.1 g/cm3).



Fig. 1. Schematic of the straw R-D process

Model for Estimating the Productivity of the R-D Process The material grabbing condition

The frictional effect that exists between the ring die, roller, and the material is the

key factor that influences the straw briquetting process. Before the material is grabbed, it

is in a sliding friction state together with the roller. There are three forces acting on the

forming material: the pressure force Nr, the friction force Fr of the roller surface on the

straw material, and the pressure force NR of the compressed straw layer on the loose

material. The closer the minimum spacing between the roller and ring die, the greater the

value of NR. When Fr is greater than the circumferential tangential component of NR, the

material is grabbed. The grabbing process is illustrated in Fig. 2a.

Fig. 2. Schematic diagram of the straw grabbing process. (a) The material grabbing process and (b) the force analysis of the grabbed straw

Force analysis is carried out for a small part of material that is about to be grabbed.

A coordinate system was established as shown in Fig. 2b. When decomposing NR along the

x and y directions and when the grab condition is met, Eq. 1 is established.

sinr RF N (1)

Based on the force equilibrium condition, Nr=NRcosθ; Nr and Fr follow the

relationship Fr=fNr, where f is the friction coefficient between the material and the roller,

and tanφ=f, where φ is the friction angle. From Eq. 1, Eq. 2 then is set up.

tan tan (2)

a b



φ is a fixed constant once the material property and roller surface state are

determined. In triangle OO1K and according to the sine theorem, β can be determined by

Eq. 3.

arcsin sinr

R r

(3)

In Fig. 2a, α=β+θ, which means that in the range of α, the straw material is grabbed

and compressed. Set R/r =λ, and since φ and θ are in the range of 90°, αmax can be expressed

as Eq. 4. The value of αmax was affected by friction angle φ and λ and a larger αmax value

corresponds to a bigger volume of the compressed raw material. There was a positive

correlation between briquetting efficiency and αmax.

max

sinarcsin

1

(4)

The Model

The variation trend of productivity is considered with reference to the change of α.

As shown in Fig. 2, material starts to be grabbed at point K, with a material height of hmax,

and hmax=R—OK. In triangle OO1K, OK can be determined by the cosine theorem, and hmax

is calculated by Eq. 5.

2

max max2 2 1 cosh r (5)

Then productivity Q (average material flow per hour through the ring die) can be

calculated by the following Eq. 6,

22

maxQ Kn B R R h

(6)

where n is spindle speed (r/min), ρ is material initial density (g/cm3), B is the effective

working width of the roller (mm), ε is the opening ratio of the ring die, K is the total number

of rollers, ξ is the material effective fill factor, and ξ is the correction factor of Eq. 6 with

a general value of 0.4 to 0.7.

Taking Eq. 4 and Eq. 5 into Eq. 6, and unifying the dimensions, the productivity Q

can be determined using Eq. 7.

2

10

2

sin1.2 10 1 1 cos( arcsin )

1

RQ Kn B

(7)

It can be seen from Eq. 7 that the productivity Q is mainly related to die structure

(ring die and roller radius ratio λ) and friction angle φ. For the straw R-D machine, the λ

value is generally between 2 and 4. The friction coefficient between the straw material and

roller are generally between 0.4 and 0.5(φ 20 to 30°). Taking ξ=0.5, ε=0.85, n=160 r/min,

B=30 mm, ρ=0.075 g/cm3, R=320mm, φ=20~30°, and λ=2~4, and using Eq. 7, the variation

of Q is shown in Fig. 3.



Fig. 3. The variation trend of productivity Q

It can be seen from Fig. 3 that a larger φ and smaller λ corresponds to a higher

productivity. It should be noted that the actual productivity Q will be different than the

theoretical calculation from Eq. 7 due to the impact of material property, uniformity of the

feeding process, and other various aspects.

Model for Mechanics of the Briquetting Process Partition of the forming process

Once the material has been grabbed and completely compressed into the die holes,

the forming process can be divided into two phases: the compression deformation stage

and the extrusion forming stage. The compression deformation stage can be described as

loose material filling the cavity and gradually compacting after the grabbing condition has

been met. The pressure of the roller increases rapidly, and then straw material is pushed

into a smaller gap region by the frictional force of the roller surface. Material density

increases until reaching the requirement during this process. The extrusion forming stage

begins once the required density is achieved. Straw is gradually pushed into the die holes

under the strong pressure from the roller. The material will not be further compacted in this

phase, and the applied pressure is maintained constant and only the shape changes (Wu et

al. 2013). The partition is shown in Fig. 4 (0 to α1 is the extrusion forming zone, and α1 to

αmax is the compression deformation zone).

Fig. 4. Schematic of the partition

Assuming that the material starts compressing at point K and reaches the required

density ρ1 at point K1, the material height here is h1 and wrap angle is α1. Since 2R≫h1 and

2R≫h, according to the productivity model, Eq. 8 was established.



01 max

1

h h

(8)

Using Eq. (5), h1 can be evaluated; therefore, the value of α1 can be obtained by Eq.

(9).

0 max 0 max

1 1

1

2

arccos 12 2

h h

r r

(9)

After the partition is determined, a further force analysis of these two areas should

be accomplished.

Force analysis of the roller

The active component of the straw R-D machine is the roller, while in the case of a

pellet mill it is the ring die. There are some certain differences of the force conditions. The

forces acting on the roller include F and N, which are the forces that the driving shaft acts

on the center of the roller; N1 and N2 represent the pressure generated on the surface of the

roller and on the two opposite direction friction forces F1 and F2, and are attributed to the

material’s compaction in compression deformation and extrusion forming regions

respectively. The directions of friction forces F1 and F2 are contrary in the two areas for

the following reason: the roller spins around point O driven by the spindle, with the straw

material generating the friction force F2 to prevent the roller from turning. Under the action

of F2, the roller rotates in the counter-clockwise direction, so the straw material is grabbed

and a frictional force F1 opposite to the rotation direction is generated. The force condition

is shown as Fig. 5.

Fig. 5. Force condition of the roller

According to the moment equilibrium condition in Fig. 5, the moment of each force

to point O1 is zero. Then it can be concluded that F1=F2. This means that the frictional force

value of the compression deformation and extrusion forming zones are equal. This analysis

well explains the rotation behavior of the roller in normal work state.



Solution of driving torque T

In the compression deformation zone, stress σαx increases from zero to the

maximum value gradually, but in the extrusion forming zone stress σmax remains constant.

In order to determine the value of N1 and N2, force analysis of a small segment of the roller

was performed (Jin 2010) and is shown in Fig. 6.

Fig. 6. Solving schematic diagram of N1 and N2

Assuming that the stress is σαx, then the pressure force dN acting on the roller can

be expressed as Eq. 10.

xdN Brd (10)

The quantities αN2 and αN1 are the central angles of resultant forces N2 and N1, respectively

(Fig. 5). They can be determined by Eqs. 11 and 12.

2 1 2N (11)

1 1

1 11

x

N

x

dN d

dN d

(12)

Because the working surface of the roller has a certain curvature, dN should be

decomposed along the αN1 (or αN2) direction for solving the resultant force N1 (or N2), as

shown in Fig. 7.

Fig. 7. Decomposition diagram of the roller force



N1 and N2 can then be calculated by Eqs. 13 and 14 (Wu and Sun 2013).

max 1

1 1

1 1 1cos( ) cos( )N

N

x N x NN Brd Brd

(13)

21

2

2 max 2 max 2

0

cos( ) cos( )N

N

N NN Brd Brd

(14)

The moment of each force to point O can be represented by Eq. 15.

1 1 2 2

1 1 2 2

cos cos

sin sin 0

N N

N N

F R r F r R r F r R r

N R r N R r

(15)

Since F1=F2 and F2=N2f, F can be determined by Eq. 16.

2 2 1 1 1 2 2cos cos sin sinD N N N NF N f N N

(16)

Then, driving torque T can be calculated by Eq. 17.

2 ( )T F R r (17)

Calculation Model of σαx

Determining the value of torque T requires the solution of σαx. Typically, there are

two main calculation methods for determining σαx: a mechanical model based on material

compaction and a calculation model based on die-hole pressure. The main differences

between these two models are the change trend of σαx and value of σmax.

The mechanical models based on material compaction, model 1, are listed in Table

1. An exponential relationship has been discovered between pressure and compacted

density, as Table 1 shows.

Table 1. Mechanical Model Based on Material Compaction

No.

Representative scholars Calculation model

1 Skalweit (Huo 2013) 𝑃 =𝑝0𝛾0

b𝛾b

2 Faborode (Faborode and O’Callaghan 1986)

𝑃 =𝐴𝛾0𝑏

[e𝑏(𝛾−1) − 1]

3 Panelli-Filho (Panelli and Filho 2001) ln (1

1 − 𝛾) = 𝑏 + 𝐴√𝑃

4 Jianjun Hu (Hu 2008) 𝑃 = 𝐴e𝑏x Note: P is pressure, γ is compacted density, p0 is initial stress, γ0 is initial density, A and b are test coefficients, and x is compaction displacement

In the Hu model (Hu 2008), rice straw was compressed and the test coefficients



were obtained. The research object in this study was rice straw, so this model was adopted

and σαx can be described by Eq. 18.

max( )x

b h hAe

(18)

Based on the elastic-plastic mechanic theory, Holm et al. (2011) provides an

effective method for calculating the die-hole pressure (Model 2). The pressure σmax at the

inlet of the die hole can therefore be calculated by Eq. (19).

2 /0 0max

hf L r

L e

(19)

where μ is Poisson’s ratio; σ0 is pre-stressing pressure; f is friction coefficient; rh is die hole

diameter; and L is die hole length. The assumption: raw material is elastic and orthotropic

material; the differential force is constant over the cross-sectional area πr2.

Wu et al. (2013) indicated that the change law of pressure σαx is in accordance with

a quadratic curve model within the scope of α1 to α. The assumptions were as follows: ring

die and roller were rigid bodies; body force was not taken into account; the material was

distributed on the ring die uniformly; and the modified Drucker-Prager-Cap model was

adapted. So σαx can be calculated by Eq. 20 (ht=hmax - h1).

2maxmax2

( )xt

h hh

(20)

A case analysis of the theoretical model

According to the formulas above, a theoretical calculation was carried out in

accordance with the actual parameters. Calculation conditions are as follows. Equipment

structure parameters: r = 320 mm, R = 720 mm, B = 30 mm, L = 165 mm, and rh = 30 mm.

Material property parameters: ρ0 = 0.075 g/cm3, ρ1 = 1.02 g/cm3, φ = 25° (f = 0.466), and u

= 0.45. Parameters of the Hu model are A = 0.1002 and b = 0.0710 (Hu 2008). The

correction factor ζ in Eq. (6) and pre-stressing pressure σ0 in Eq. (18) have been obtained

through testing prior to the calculation (ζ is 0.47 and σ0 is 0.1895 MPa). Variation of σαx

based on two models in the compression deformation zone is shown as Fig. 8. Calculation

results of the two models are shown in Table 2.

Fig. 8. Variation of σαx in the compression deformation



Table 2. Calculation Results of the Two Models

Parameter name Model 1 Model 2

Q (t/h) 1.089

αmax (°) 44.761

h (mm) 53.496

h1 (mm) 3.934

α1 (°) 12.066

αN1 (°) 21.074 21.499

αN2 (°) 6.033 6.033

N1 (N) 11570.612 9106.450

N2 (N) 7019.541 7660.822

F (N) 5098.756 4371.149

T (N•m) 4079.005 3402.711

Experimental Verification To verify the accuracy of the theoretical model, productivity and torque testing

were completed. Productivity testing was performed by digital electronic weight

(according to the agricultural industry criteria of China NY/T 1883-2010), and torque

testing of the drive motor’s shaft was implemented by the Bichuang wireless torque

measurement system (Beijing Bichuang Technology Co., Ltd., Beijing, China). In this

system, strain gauges were symmetrically arranged to eliminate the impact of bending

moment. The arrangement method and bridging form of strain gauge are shown in Fig. 9a.

Experimental equipment and materials include a ring-die straw briquetting machine

(9EYK1800; Jiangsu ENERGY Renewable Resources Co., Ltd., Taizhou, Jiangsu

Province, China), wireless nodes (TQ201; Beijing Bichuang Technology Co., Ltd., Beijing,

China), digital electronic weighter, special torque strain gages, wireless gateway, special

torque analysis software, sandpaper, alcohol cotton, glue, scissors, and fiber tape. The raw

material was rice straw harvested in the autumn of 2013 in Jiangyan, Jiangsu Province,

China. The straw was chopped, with particle size of 2 to 20 mm and moisture content of

15 to 21%, and briquetted without adding any binders. Experiments were conducted at an

industrial factory (Jiangsu ENERGY Renewable Resources Co., Ltd., Taizhou, Jiangsu

Province, China). Figure 9b shows the torque testing site.

Fig. 9. Torque testing program. (a) Arrangement and bridging form of strain gauge and (b) torque

testing site

a

b



RESULTS AND DISCUSSION

Figure 10 shows the torque testing data. The average value of the motor shaft’s

testing torque TM was 0.729 kN•m and the roller spindle’s testing torque T was 3.187 kN•m

(T = iηTM, where η is transmission efficiency and i is transmission ratio; i = 4.6, η = 0.95

for the testing machine).

Fig. 10. Experimental torque data. Data is expressed as average ± SD

Experimental results and deviations are shown in Table 3. The testing value of

productivity Q was 1.041 t/h, the average of three test results. There was a deviation

(between the calculated and tested values) of 4.61% due to the impact of the feeding

process (rice straw contains lignin and cellulose; they are very soft and can easily entwine

together. Therefore, small groups of straw material are formed one after another during the

feeding). Fluctuation of torque T in Fig. 10 shows the non-uniformity of the actual feeding

process. Therefore, the deviation is within an acceptable range. Compared with Model 1,

Model 2 exhibited a better accuracy with the deviation (between the calculated and tested

values) of 6.76%, which means that Model 2 can describe the mechanical behavior of straw

actual compression process more accurately.

Table 3. Experimental Results and Deviation

Category Productivity Q (t/h) Torque T (N•m)

Tested value 1.041 3187.153

Calculated value 1.089 Model 1 Model 2

4079.005 3402.711

Deviation 4.61% 27.98% 6.76%

CONCLUSIONS

This work was aimed at reducing the energy consumption and improving the

efficiency of the straw briquetting process. Based on the theoretical derivation and

experimental validation, the key conclusions are summarized as follows:

1. Productivity Q is higher at smaller die structure (radius ratio λ) and larger friction angle

φ. The forming process can be divided into two stages: compression deformation and

then extrusion forming. Two stages are corresponding at 0 to α1 and α1 to αmax during

the process, respectively.



2. The forces acting on the roller include F and N, for which the driving shaft acts on the

center of the roller; N1 and N2 represent the pressure generated on the surface of the

roller and on the two opposite direction friction forces F1 and F2.

3. In the compression deformation zone, stress σαx increases from zero to the maximum

value gradually, but in the extrusion forming zone stress σmax remains constant. There

are two main calculation methods for σαx: a mechanical model based on material

compaction and a calculation model based on die-hole pressure.

4. Experimental validation indicates that the productivity model was successful since the

deviation was calculated to be 4.61%. The torque model determined by the calculation

model based on the die-hole pressure had a better accuracy with a deviation of 6.76%.

ACKNOWLEDGMENTS

This work was supported by The Project of Six Talents Peak of Jiangsu Province

(2010-JXQC-080), The Natural Science Foundation of Jiangsu Province (BK2011706),

and The Prospective Industry-Study-Research Cooperation Foundation of Jiangsu

Province (BY2012023).

REFERENCES CITED

Adapa, P. K., Tabil, L. G., and Schoenau, G. J. (2013). “Factors affecting the quality of

biomass pellet for biofuel and energy analysis of pelleting process,” Int. J. Agric.

Biol. Eng. 6(2), 1-12. DOI: 10.3965/j.ijabe.20130602.001

Cong, H. B., Zhao, L. X., Yao, Z. L., Tian, Y. S., and Meng, H. B. (2013). “Analysis on

capacity and energy consumption of biomass circular mould granulator,” Trans. Chin.

Soc. Agric. Machinery (Nongye Jixie Xuebao) 44(11), 144-149.

Duan, J., Chen, S. R., Yao, Y., and Jiang, X. X. (2013). “Energy consumption test and

process optimization for circular mold briquetting machine,” Trans. Chin. Soc. Agric.

Machinery (Nongye Jixie Xuebao) 44(S1), 149-155.

Faborode, M. O., and O’Callaghan, J. R. (1986). “Theoretical analysis of the compression

of fibrous agricultural materials,” J. Agric. Eng. Res. 35(3), 175-191. DOI:

10.1016/S0021-8634(86)80055-5

Ghadernejad, K., and Kianmehr, M. H. (2012). “Effect of moisture content and particle

size on energy consumption for dairy cattle manure pellets,” Agric. Eng. Int.: CIGR J.

14(3), 125-130.

Gillespie, G. D., Everard, C. D., Fagan, C. C., and McDonnell, K. P. (2013). “Prediction

of quality parameters of biomass pellets from proximate and ultimate analysis,” Fuel

111, 771-777. DOI: 10.1016/j.fuel.2013.05.002

Holm, J. K., Stelte, W., Posselt, D., Ahrenfeldt, J., and Henriksen, U. B. (2011).

“Optimization of a multiparameter model for biomass pelletization to investigate

temperature dependence and to facilitate fast testing of pelletization behavior,” Energ.

Fuel 25(8), 3706-3711. DOI: 10.1021/ef2005628

Huo, L. L. (2013). Study on Forming Mechanism of Biomass Pellet and Process

Optimization of Pellet Mill, Ph.D dissertation, China Agricultural University, Beijing,

China.



Hu, J. J. (2008). “Straw pellet fuel cold molding by compression: Experimental study and

numerical simulation,” Ph.D dissertation, Dalian University of Technology, Dalian,

China.

Hu, J. J., Lei, T. Z., Sheng, S. Q., and Zhang, Q. G. (2013). “Specific energy

consumption regression and process parameters optimization in wet-briquetting of

rice straw at normal temperature,” BioResources 8(1), 663-675.

Jin, Z. (2010). Engineering Mechanics, Southeast University Press, Nanjing, China.

Karunanithy, C., Wang, Y., Muthukumarappan, K., and Pugalendhi, S. (2012).

“Physicochemical characterization of briquettes made from different feedstocks,”

Biotechnol. Res. Int. 2012, 1-12. DOI:10.1155/2012/165202

Kaliyan, N., and Morey, R. V. (2010). “Densification characteristics of corn cobs,” Fuel

Process Technol. 91(5), 559-565. DOI: 10.1016/j.fuproc.2010.01.001

Panelli, R., and Filho, F. A. (2001). “A study of a new phenomenological compacting

equation,” Powder Technol. 114(1), 255-261. DOI: 10.1016/S0032-5910(00)00207-2

Panwar, V., Prasad, B., and Wasewar, K. L. (2010). “Biomass residue briquetting and

characterization,” J. Energ. Eng.-ASCE 137(2), 108-114. DOI:

10.1061/(ASCE)EY.1943-7897.0000040

Song, X., Zhang, M., Pei, Z. J., and Wang, D. (2014). “Ultrasonic vibration-assisted

pelleting of wheat straw: A predictive model for energy consumption using response

surface methodology,” Ultrasonics 54(1), 305-311. DOI:

10.1016/j.ultras.2013.06.013

Ståhl, M. and Berghel, J. (2011). “Energy efficient pilot-scale production of wood fuel

pellets made from a raw material mix including sawdust and rapeseed cake,” Biomass

& Bioenerg. 35(12), 4849-4854. DOI: 10.1016/j.biombioe.2011.10.003

Stelte, W., Sanadi, A. R., Shang, L., Holm, J. K., Ahrenfeldt, J., and Henriksen, U. B.

(2012). “Recent developments in biomass pelletization - A review,” BioResources

7(3), 4451-4490.

Tuo, H. F. (2013). “Energy and energy-based working fluid selection for organic Rankine

cycle recovering waste heat from high temperature solid oxide fuel cell and gas

turbine hybrid systems,” Int. J. Energ. Res. 37(14), 1831-1841. DOI: 10.1002/er.3001

Wu, K., Sun, Y., Peng, B. B., Ding, W. X., and Wang, S. H. (2013). “Modeling and

experiment on rotary extrusion torque in ring-die pelleting process,” Trans. Chin.

Soc. Agric. Eng. (Nongye Gongcheng Xuebao) 29(24), 33-39. DOI:

10.3969/j.issn.1002-6819.2013.24.005

Wu, K., and Sun, Y. (2013), Ring-die Pellet Forming Technology and Equipment,

Science Press, Beijing, China.

Yao, Z. L., Zhao, L. X., Tian, Y. S., Meng, H. B., and Pang, L. S. (2013). “Study on

biomass briquetting machines with vertical ring die,” Trans. Chin. Soc. Agric.

Machinery (Nongye Jixie Xuebao) 44(11), 139-143. DOI: 10.6041/j.issn.1000-

1298.2013.11.025

Zhang, B. L., Wang, X. T., and Yang, S. G. (2008). “Key problems in production and

application of straw densification briquetting fuel (SDBF),” Trans. Chin. Soc. Agric.

Eng. (Nongye Gongcheng Xuebao) 24(7), 296-300.

Article submitted: July 10, 2014; Peer review completed: August 9, 2014; Revised

version received: August 25, 2014; Accepted: August 26, 2014; Published: September 2,

2014.

peer-reviewed article bioresources · peer-reviewed article bioresources.com xia et al. (2014)....

Documents